This application is related to Japanese patent application No. HEI 11(1999)-30155 filed on Feb. 8, 1999 whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The preset invention relates to a semiconductor laser device and a method of manufacturing the semiconductor laser device, and more particularly to a semiconductor laser device to be used for an optical information recording and reproducing apparatus and a method of manufacturing the semiconductor laser device.
2. Description of the Related Art
A DVD (Digital Versatile Disk) which is a next generation optical disk is characterized by the reproduction of dynamic images for 135 minutes as video recording and a capacity of 4.7 gigabytes as information recording and the like.
In a DVD reproducing apparatus, it is desired that the reproducing and data reading operations of a CD, a CD-ROM and a CD-R which have conventionally been used widely can be carried out in addition to the reproducing and data reading operations of a DVD (video recording), a DVD-ROM (informations recording) and a DVD-R (information recording using one-time writing).
However, since the DVD is greatly different from the CD in the following two respects, it has difficulties in obtaining the compatibility of a system.
In a first respect, while a substrate of a disk of the CD has a thickness of 1.2 mm, that of a disk of the DVD has a thickness of 0.6 mm. The reason is that a tolerance to the inclination of the disk should be kept when the NA (numerical aperture) of a collective lens is increased to raise a recording density.
In a second respect, the oscillation wavelength of a semiconductor lasers to be used for a pick-up is given. A collective spot diameter on the disk is proportional to the wavelength. Therefore, the CD uses a semiconductor laser having a 780 nm band (an infrared region), while the DVD uses a semiconductor laser having a 650 nm band (a red region) in order to implement high density recording.
For the pick-up for reading information recorded on the disk, the two kinds of disks having different substrate thicknesses are obstacles to the aberration of an Optical system. As a solution, the following method is currently known
Examples of the solution include a method using two lenses for the CD and the DVD by switching, a method using a bifocal lens, a method using a liquid crystal shutter and the like (see Electronic Material, the June issue in 1996, pp. 38). By using these methods, the information of the disks having different substrate thicknesses can be read out and the reading operations of the CD and CD-ROM can be carried out by the DVD reproducing apparatus.
According to the above-mentioned methods, however, the information of the CD-R used for a method of recording a dye reacting to light having a 780 nm band cannot be reproduced by the DVD reproducing apparatus including a light source having a 650 nm band. For this reason, the following methods have been proposed as a pick-up for a DVD capable of reproducing the information of the CD-R.
As a first method, a pick-up for a CD (using a laser having a 780 nm band) and a picks-up for a DVD (using a laser having a 650 nm band) are provided in a reproducing apparatus. In this case, however, the apparatus becomes large-sized and a cost is increased.
As a second method, a semiconductor laser emitting light having two kinds of wavelengths is incorporated in one pick-up. The following method has been proposed.
{circle around (1)} Two kinds of laser chips having different oscillation wavelengths are provided in a semi conductor laser package (see Japanese Laid-Open Patent Publication No. Hei 11(1999)-97804).
{circle around (2)} By changing a thickness of a coating film for adjacent resonators of one laser chip, an oscillating operation is carried out with different wavelengths (see Japanese Laid-Open Patent Publication No. Hei 3(1991)-9589).
{circle around (3)} For adjacent resonators of one laser chip, the width of a groove provided under an active layer is varied and the Al content of the active layer is varied. Thus, an oscillation wavelength is changed (see Japanese Laid-Open Patent Publication No. Sho 61(1986)-19186).
In the case where a semiconductor laser emitting light having two kinds of wavelengths is thus incorporated in one pick-up, a distance between light emitting spots causes troubles in the above-mentioned {circle around (1)}. More specifically, a distance between light emitting spots should be at least 100 xcexcm or less in order to treat the light having two different wavelengths by using the same lens in an optical system of a pick-up. However, it is usually hard to set the distance between the light emitting spots to 100 xcexcm or less in order to arrange two independent laser chips in a package in parallel, and an error of approximately several tens xcexcm is also made during the arrangement.
In the above-mentioned {circle around (2)} and {circle around (3)}, moreover, since two light emitting points are simultaneously formed at the one-time crystal growing step, the active layer is formed of the same component. Consequently, a difference in a wavelength of approximately 10 nm is made between the two light emitting points by using any method. Therefore, it is impossible to implement two oscillation wavelengths of 650 nm and 780 nm which are necessary for the DVD and the CD.
In consideration of such circumstances, it is an object of the present invention to provide a semiconductor laser device capable of generating laser beams in an infrared region and a red region at a distance between close light emitting spots and a method of manufacturing the semiconductor laser device.
The present invention provides a semiconductor laser device wherein a plurality of semiconductor laser resonators having light emitting layers using materials different from each other are provided on the same semiconductor substrate in parallel with a main surface of the semiconductor substrate and a high-resistance region is provided between the semiconductor laser resonators.
According to the present invention, the semiconductor laser resonators having the light emitting layers using materials different from each other are arranged in parallel with the main surface of the semiconductor substrate. Therefore, it is possible to generate a plurality of laser beams in different wavelength regions at a distance between close light emitting spots in parallel.
According to the present invention, the laser beams in the infrared and red regions can be generated at the distance between the close light emitting spots by using a single semiconductor laser device.
This object as well as other objects, features and advantages of the invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings.